2-Oxoglutarate (2OG) and Fe(II)-dependent dioxygenases (2OG-oxygenases) are known to catalyse the hydroxylation of protein, lipid and nucleic acid substrates. They are involved in a variety of medicinally important biological processes including collagen biosynthesis, chromatin modification and hypoxia signalling. These hydroxylation reactions can result in either stable incorporation of a hydroxyl group, or in the case of N-methyl group hydroxylation, the formation of an unstable intermediate that decomposes into formaldehyde. The latter reaction is employed by 2OG-oxygenases that catalyse N-demethylation reactions of nucleic acids and proteins.
The human genome contains approximately 60 genes predicted to encode 2OG-oxygenases, many of which are not characterised in terms of their substrates. Proteins of this gene family can be subdivided into groups based on similarity within the catalytic motif. For example, the Hypoxia Inducible Factor (HIF) prolyl hydroxylases consists of three 2OG-hydroxylases (PHD1-3 or EGLN1-3 enzymes) that target the Hypoxia Inducible transcription Factor (HIF) for proteolytic degradation. The JmjC histone demethylase subfamily members catalyse the demethylation of specific lysine residues within the N-terminal tails of histone proteins and are involved in the regulation of chromatin structure and gene expression.
The Factor Inhibiting HIF (FIH), is an asparaginyl hydroxylase that, like PHD1-3, also targets HIF. FIH-mediated hydroxylation of the HIF C-terminal transactivation domain (CAD) mediates oxygen-sensitive regulation at the transcriptional activity. Recently, it was reported that FIH catalyses the hydroxylation of histidinyl residues within the ankrin repeat domains. FIH is one of a family of human 2OG oxygenases related to the Jmjc subfamily. Other members of this family that have been assigned 2OG-oxygenase activity include JMJD6. Although comparatively little is known about the activity and function of the FIH sub-group of 2OG-oxygenases (compared to the PHD1-3 or Jmjc subfamily), they are of significant interest due to the fact that they are implicated in pathological processes in cells, or are abnormally expressed in disease, and particularly in cancer.
MINA53 is a 2OG/Fe(II)-dependent dioxygenase originally identified in a microarray screen for Myc target genes overexpressed in glioblastoma cells. MINA53 overexpression was subsequently observed in a variety of tumour types and is often associated with poor prognosis. MINA53 has been implicated in several biological and pathologically relevant processes implicated in tumourigenesis, including cell proliferation, apoptosis, and invasion. MINA53 shares significant sequence homology with a closely related human 2OG/Fe(II)-dependent dioxygenase known as NO66. Like MINA53, NO66 has also been implicated in cancer: It is overexpressed in non-small cell lung cancer and it regulates apoptosis and proliferation in vitro Tsuneoka et al, J. Biological Chem 2002, 277, 35450-35459, Komiya et al, J. Cancer Res Clin Oncol, 2010, 136, 465-473, Stry et al, Nat Immunol, 2009, 872-879.
MINA53 and NO66 are primarily localised to the nucleolus and are negatively regulated by mitogen withdrawal and RNA Polymerase I inhibition. Proteomic analyses identify these enzymes in complex with a variety of ribosomal and nucleolar proteins. Together, these observations implicate MINA53/NO66 in ribosomal biogenesis/function and/or protein translation: Over-activation of these processes are hallmarks of tumour cells, Eilbracht et al, Mol Biology of the Cell, 2004, 15, 1816-1832, Sinha et al, EMBO J, 2010, 29, 68-79.